pub fn new_birthday_probability(n: u32) -> f64 {
    if n < 2 {
        return 0.0;
    }

    let days = 365.0;

    let prob = (0..n).fold(1.0, |acc, i| acc * (days - i as f64) / days);

    ((1.0 - prob) * 10000.0).round() / 10000.0
}
